SHARE ARTICLE

Late Season Soybean Management

Keeping a soybean crop healthy, even late in the season, is important for maximizing yield potential.

Reducing insect, disease, and weed pressure, nitrogen deficiency, and drought stress during the critical growth stages for soybean development can help prevent potential yield loss.

Early canopy development can increase flowering time and number of main-stem nodes.

Proper disease and insect identification is a critical management step.

Soybean Insects

Soybean aphids (Aphis glycines) are considered the dominant insect pest in soybean fields. Aphids are small, 1.5 mm long, and range from pale yellow to lime green in color. Adults have distinct black cornicles. They are usually found in soybean fields from late May through August. Aphids have piercing-sucking mouthparts that are used to suck fluids from the plant. Although they feed on leaves, stems, and pods they are most often found on the underside of leaves.1 Heavy infestations can result in the stunting of plant growth and development, which can reduce yield potential. If feeding continues through the pod filling stage, pod set may be affected and plants may produce fewer seeds per pod.2 As much as 50% yield reductions may occur in severely infested fields. However, aphid populations that are over the threshold when pods are being filled can have a greater effect on yield potential than outbreaks at R5 or R6 growth stages.

The occurrence of aphids is highly variable each season. Treatment thresholds and recommendations vary by state. Please contact your local agronomist for thresholds and apply insecticides as needed.

Figure 1. Soybean aphids.

Soybean podworm (Helicoverpa zea), also known as corn earworm, can be especially problematic in the southern growing regions of the United States. Infestation normally occurs from late July through August. It is a major pest in soybeans, corn, cotton, and grain sorghum. Small larvae are usually brown with a dark head. As the larvae grow, they change color from yellowish green to black, and the head is usually orange on large larvae. While small larvae feed on tender leaves and blooms, larger larvae feed on leaves, stems, or pods. Large populations can cause severe defoliation. Once pods begin forming, larvae feed on pods causing severe damage.

Figure 2. Soybean podworm.

Stink bugs. The three species of stink bugs mostly found in soybean fields are green stink bug (Acrosternum hilare), southern green stink bug (Nezara viridula), and brown stink bug (Euschistus servus).3 Stink bugs are shield shaped and immatures look similar to adults, but are wingless. The damage from stink bugs is caused when they insert their piercing– sucking mouthparts into the plant and extract juices. Damage is greatest when they feed on the seed in the developing pod (Figure 4). Feeding can cause pods to drop. Both adults and nymphs can cause injury to soybeans.

Frogeye leaf spot produce spots on the leaves (Figure 5), while interveinal yellowing may form with sudden death syndrome (SDS) and stem canker. Premature defoliation is also a concern with frogeye leaf spot, phytophthora root rot and stem canker. Since pod set through seed fill stages (R3 through R6) are the most critical period for yield potential, leaf loss can significantly reduce yield potential. Healthy, green plant material is necessary for photosynthesis and converting sugars for pod fill; therefore, it is important to protect the leaf tissue.

Figure 5. Frogeye leaf spot.

Pod and stem blight can be found on stems, petioles, and pods in the late reproductive stages as irregularly-shaped brown blotches. Infection on pods may result in fewer or smaller seeds per pod. Leafdefoliation is also an issue if infestation is severe.

Symptoms of stem canker first appear during the early reproductive stages as small, red-brown lesions (Figure 7). Initial lesions are usually found near a lower leaf node and expand lengthwise as the season progresses. Lesions eventually girdle the stem, causing wilting and plant death.

Fungicide applications should be considered if the infestation has reached threshold levels during pod developmental stages (R3 to R5). Spraying fungicides after R6 is generally not recommended.

Tips for Proper Fungicide Application. Soybean diseases usually start in the lower canopy and move into the middle, then upper canopy as the crop matures. Therefore, fungicide applications need to be placed as deep into the canopy as possible. Sprayer reconfiguration is necessary to obtain good coverage and canopy penetration. Using a spray volume of no less than 15 gallons per acre is important to provide good coverage, especially later in the season when the canopy is deeper and denser. Nozzle type, spray pressure, application volume, and speed will determine the uniformity of spray deposition and penetration into the canopy.5 Flat-fan pattern nozzles are generally the best choice, provided the spray from these nozzles is characterized as high-fine to mid-medium (200 to 300 micron droplets in diameter). Proper nozzle orientation and overlap is also critical to achieve optimum spray deposition.

Weed Management

Weeds compete with the crop for light, moisture, and nutrients and can be a yield-limiting factor. For increased yield potential, weeds must be controlled between V1 and V3 soybean stage. This is usually referred to as the critical time for weed control.7 Early season weed control is important for early canopy development and maximizing yield potential in soybeans. Plants that develop canopies early may have an increase in flowering time and number of main-stem nodes. Weeds that emerge later in the season have little direct effect on yield potential, but may interfere with harvesting and add foreign matter to the harvested crop. Although good early-season weed control is critical for optimum yield potential, sometimes situations arise where in -season weed management is warranted. Over-the-top applications can be used in controlling late-germinating weeds and weeds not controlled by preplant or preemergence herbicides.7 If a herbicide application is necessary, choose the chemistry depending upon the type of weed(s) present in the field.

Water Stress

Water demand is highest for soybean plants during pod development (R3 to R4) and seed fill (R5 to R6). Moisture stress from flowering through the pod fill stage can severely reduce yield potential by producing smaller or fewer seeds or both.8

Nitrogen Application

Since a soybean plant produces nutrient rich, high protein seed, nitrogen (N) requirements for this crop are rather high. Peak N demand in soybean production is during pod fill and fixed N alone may not be enough to meet plant demand. Both soil N and fixed N may be necessary for maximum soybean yield potential. Research shows that supplemental N during these pod fill may increase yield potential.

Summary

Scouting soybean fields late in the season can help identify problems that may be controlled through targeted management strategies and may offer insight for the next growing season. Look for insect damage, weed escapes, and signs of diseases. Late-emerging weeds can cause harvest losses and increase moisture and trash content at harvest. Fields should be monitored for pod-feeding insects through R7 growth stage. Late-season irrigation is recommended to have adequate soil moisture to ensure maximum seed weight. A fungicide application is warranted when disease incidence reaches threshold levels.

XtendiMax® herbicide with VaporGrip® Technology is part of the Roundup Ready® Xtend Crop System and is a restricted use pesticide. ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. It is a violation of federal and state law to use any pesticide product other than in accordance with its labeling. XtendiMax® herbicide with VaporGrip® Technology and products with XtendFlex® Technology may not be approved in all states and may be subject to use restrictions in some states. Check with your local product dealer or representative or U.S. EPA and your state pesticide regulatory agency for the product registration status and additional restrictions in your state. For approved tank-mix products and nozzles visit XtendiMaxApplicationRequirements.com.

Commercialization is dependent on multiple factors, including successful conclusion of the regulatory process. The information presented herein is provided for educational purposes only, and is not and shall not be construed as an offer to sell, or a recommendation to use, any unregistered pesticide for any purpose whatsoever. It is a violation of federal law to promote or offer to sell an unregistered pesticide.

Do not export Roundup Ready® Alfalfa seed or crop, including hay or hay products, to China pending import approval. In addition, due to the unique cropping practices do not plant Roundup Ready® Alfalfa in Imperial County, California, pending import approvals and until Forage Genetics International, LLC (FGI) grants express permission for such planting.

Forage Genetics International, LLC (“FGI”) is a member of Excellence Through Stewardship® (ETS). FGI products are commercialized in accordance with ETS Product Launch Stewardship Guidance, and in compliance with FGI’s Policy for Commercialization of Biotechnology-Derived Plant Products in Commodity Crops. Certain products have been approved for import into key export markets with functioning regulatory systems. Any crop or material produced from this product can only be exported to, or used, processed or sold in countries where all necessary regulatory approvals have been granted. It is a violation of national and international law to move material containing biotech traits across boundaries into nations where import is not permitted. Growers should talk to their grain handler or product purchaser to confirm their buying position for this product. Growers should refer to http://www.biotradestatus.com/ for any updated information on import country approvals. Excellence Through Stewardship® is a registered trademark of Biotechnology Industry Organization.

Monsanto Company is a member of Excellence Through Stewardship® (ETS). Monsanto products are commercialized in accordance with ETS Product Launch Stewardship Guidance, and in compliance with Monsanto’s Policy for Commercialization of Biotechnology-Derived Plant Products in Commodity Crops. This product has been approved for import into key export markets with functioning regulatory systems. Any crop or material produced from this product can only be exported to, or used, processed or sold in countries where all necessary regulatory approvals have been granted. It is a violation of national and international law to move material containing biotech traits across boundaries into nations where import is not permitted. Growers should talk to their grain handler or product purchaser to confirm their buying position for this product. Excellence Through Stewardship® is a registered trademark of Excellence Through Stewardship.

ALWAYS READ AND FOLLOW DIRECTIONS FOR USE ON PESTICIDE LABELING. IT IS A VIOLATION OF FEDERAL AND STATE LAW to use any pesticide product other than in accordance with its labeling. NOT ALL formulations of dicamba or glyphosate are approved for in-crop use with Roundup Ready 2 Xtend® soybeans. ONLY USE FORMULATIONS THAT ARE SPECIFICALLY LABELED FOR SUCH USES AND APPROVED FOR SUCH USE IN THE STATE OF APPLICATION. Contact the U.S. EPA and your state pesticide regulatory agency with any questions about the approval status of dicamba herbicide products for in-crop use with Roundup Ready 2 Xtend® soybeans.

Roundup Ready 2 Xtend® soybeans contains genes that confer tolerance to glyphosate and dicamba. Glyphosate will kill crops that are not tolerant to glyphosate. Dicamba will kill crops that are not tolerant to dicamba. Glufosinate will kill crops that are not tolerant to glufosinate. Contact your Monsanto dealer or refer to Monsanto’s Technology Use Guide for recommended weed control programs.

B.t. products may not yet be registered in all states. Check with your Monsanto representative for the registration status in your state.

IMPORTANT IRM INFORMATION: RIB Complete® corn blend products do not require the planting of a structured refuge except in the Cotton-Growing Area where corn earworm is a significant pest. SmartStax® RIB Complete® corn blend is not allowed to be sold for planting in the Cotton-Growing Area. See the IRM/Grower Guide for additional information. Always read and follow IRM requirements.

Performance may vary, from location to location and from year to year, as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on the grower’s fields.

The Climate FieldView™ services provide estimates or recommendations based on models. These do not guarantee results. Consult your agronomist, commodities broker and other service professionals before making financial, risk management, and farming decisions. Information and recommendations we provide do not modify your rights under insurance policies purchased through our affiliates. More information at www.climate.com/disclaimers.